CA1227931A

CA1227931A - Abrasive cutting wheel

Info

Publication number: CA1227931A
Application number: CA000458071A
Authority: CA
Inventors: Carl F. Roemmele; Joseph D. Ekland
Original assignee: Federal Mogul LLC
Current assignee: Federal Mogul LLC
Priority date: 1983-07-06
Filing date: 1984-07-04
Publication date: 1987-10-13
Also published as: ATE31505T1; GR82240B; IL72301A0; JPS6051203A; US4550708A; DE3468191D1; DE8420322U1; EP0131278A1; BR8403357A; KR850001061A; AU3032884A; EP0131278B1; ES289500U; ES289500Y

Abstract

ABSTRACT OF THE DISCLOSURE
A circular cutting wheel is disclosed and has a plurality of diamond-bearing arcuately shaped cutting members bonded to the periphery thereof and a generally U-shaped gullet between each pair of adjacent cutting members, wherein preferably the arc length of each cutting member at its radial extremity is approximately equal to the arc length of an adjacent gullet at its radial extremity, thereby providing the means with which to circulate fluid coolant to the cutting members at the point the cut is being made and to discharge the swarf from that same point to an area away from the cutting wheel.

Description

I I
-The present invention relates to abrasive saw blades or cutting wheels and, most specifically to saw blades of the type formed by a strong, air-cuter sheet metal drive core having one or more cutting 5 members containing dispersed diamond dust secured around its periphery by a metallic bond and suitable for serious industrial applications.
Diamond abrasive saws of the metallic bonded variety have been classically divided into three 10 distinct groups, all of which are well known in the trade at the present time. The first of these groups is the serrated or notched rim type blade, which is old in the art and is probably the earliest concept of the diamond cutting disc or saw This type of blade 15 is made by notching or slitting a disc of steel or copper and inserting into these fine hacks a paste of diamond grit and a holding material like petroleum jelly or, more recently, various metal powders. The notched rim type of saw has the merit of being reason-I ably indestructible, but it cuts so poorly that it has no real acceptance in any serious industrial apt placations, although it is satisfactory in the case of the lowest priced blades which are used in home hobby-type operations such as the lapidary avocation.
The second group of saw blades consists of a cutting disc having around its periphery a con-tenuous annuls of compressed and matured metallic powder containing diamond dust. This blade has been .

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traditionally made by cold molding the metal powder and diamond dust annuls around a steel body and sistering or otherwise maturing the annuls to a surf-fishnet strength to hold the diamond dust well and to 5 cut freely. This type of blade is functionally superior over the first mentioned group of blades, but it too is unsatisfactory for serious industrial applications since it has the disadvantage of being physically frail due to the delicate nature of the bond between 10 the annuls and the core. Various mechanical devices have been proposed to improve the bond, but in general due to the shortcomings of the manufacturing method, the cutting disc so made is fragile. Its use is confined in large part to precision operations such 15 as~gemanium cutting, optical glass cutting, and other nice uses that fall more or less into the instrument making classes.
The third and relatively recent group of saw blades is the discontinuous rim or segmental type.
I This cutting disc is made by manufacturing a series of short arcuate segments containing diamond powder in a metallic body. These segments are usually about 2 inches long and are ordinarily silver soldered, brazed or welded to the rim of a steel core which has 25 been divided into sections of approximately the segment length by chopping or sawing the rim radially.
Without these discontinuities, the saw disc could not readily be made owing to the great stresses created in the disk by heating only its periphery. The sex-30 minted blade has been accepted by those fields theater prone to give the hardest usage to the blades, such as the concrete sawing and masonry cutting field ; where rough abrasive cutting is done.
For such applications it is common to flush 35 the cutting area continuously during the cutting opt ~2~33~

. 1.3 -oration with a fluid coolant in order to keep the blade as cool as possible and to flush from such area loose rock like material, spent abrasive and the like all of which in combination with the coolant itself 5 is generally referred to in the art and throughout this description of the present invention as "swarm".
Even though the construction of this type of blade has been developed to a high point of perfection, blades must commonly be replaced whenever the swarm I erodes the steel drive core at the juncture of the cutting members with the core and thus causes under-cutting of the cutting members and possible loss of the cutting members. This is particularly the case in certain types of concrete cutting operations. Prior 15 to the invention of the related application referred to above, little or no thought had been given to the idea of utilizing the blade construction itself to create a more effective means of providing greater cooling of the wheel and delivering coolant to the imp 20 mediate area or point at which the wheel is making thicket as a means of flushing the swarm from that portion of the cut or cut groove which overlaps the sides of the wheel as the cut is being made.
Another recently developed segmental blade or 25 cutting wheel is that disclosed in the applicant's earlier development as described in pending patent apt placation No. 433,455 , filed 28/7/83, Although such segmental cutting wheel represents a major advancement in the art, the present invention provides even more of-on fictive means of cooling the wheel, of delivering cool-ant to the cutting portion of the wheel, and of flushing the swarm from the portion of the cut that overlaps the sides of the wheel during the cutting operation.
Accordingly, the basic aim of the invention is to provide a new and improved abrasive cutting wheel which provides a more effective means for ~2,~7~3~1.

circulating a fluid coolant, such that less abrasive material is required than conventional cutting wheels while still retaining cutting speeds at least equal to such conventional wheels.
The present invention therefore provides a rotatable cutting wheel for cutting rock or rock-like material, said cutting wheel comprising: a circular generally disc-shaped drive core having a plurality of circumferential extending and circumferential-10 spaced support surfaces, each of. said support sun-faces having affixed thereto for substantially the full circumferential length thereof an abrasive cut-tying material means capable of cutting an adradable rock or rock-like material; said core having a pour-15 amity of generally U-shaped gullets, each said U-shaped gullet therein being defined by the space be-tweet each adjacent pair of said support surfaces, said U-shaped gullet extending between a closed gullet end located a substantial radial distance inwardly 20 of said support surfaces and an open gullet end being in communication with the space between said adjacent pair of said support surfaces, the circumferential width of said open gullet end being generally co-extensive with the circumferential length of said 25 space; the ratio of said circumferential length of said adjacent pair of said support surfaces to the air-cumferential length of said space being in the range of approximately 0.75 to 1.20, the total circumferential length of said support surfaces being approximately 3Q equal to the total circumferential width of said U-shaped gullets at the open end thereof, and the radial distance between the open and closed ends of each said U-shaped gullet closely approximating the circumferen-trial width of each said open gullet end; whereby each 35 said U-shaped gullet and its respective space between adjacent support surfaces cooperate to define a fluid ~2~7~3~

passageway having a substantial volumetric capacity - through which a fluid coolant can be circulated in substantial amounts to the cutting area, can cool the drive core in the area immediately adjacent the 5 abrasive cutting material means, and can carry away swarm therefrom.
Features and advantages of this invention will become more evident from the following description of a preferred embodiment of the invention taken together 10 with the accompanying drawings wherein:
Fig. 1 is a fragmentary face view of a cutting wheel according to one example of the prior art;
Fig. 2 to a fragmentary face view of a cutting wheel according to a preferred embodiment of the in-15 vision;
Fig. 3 is a fragmentary radial cross section of the cutting wheel of Fig. 2 taken approximately on the line 3-3 thereof through a gullet; and Fig. 4 is a generally schematic perspective 20 view of the cutting system according to a preferred embodiment of the invention.
Fig. 1 illustrates a diamond abrasive cutting wheel or blade generally designated as 1, which is an example of a cutting wheel incorporating the invent 25 lion of applicant's aforesaid earlier development The illustrated example of said cutting wheel in-mention generally includes a central sheet metal drive disc or core 10 made of suitable wrought metal, preferably steel, and provided with a central apparatus 30 or arbor hole 12 for mounting the blade on a rotating axially-extending shaft. The periphery of the core is segmented so as to provide a plurality of cutting segments 14 and a gullet 16 between each adjacent pair of cutting segments 14. Upon a base or support 35 surface located at the radially extremity of each cutting segment 14 there is bonded a diamond-bearing . .

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cutting element or member 18. As viewed from the face ox the saw blade in Fig. 1, the cutting elements are arcuate, Ed the bases of the cutting segments are circular arcs having the center of the core as their 5 centers of curvature.
The gullets in the illustrated exemplary em-bodiment of the applicant's earlier development in Fig. 1 are bounded by respective side faces 20 and 22 of each adjacent pair of cutting segments 14. Each 10 pair of side faces 20 and 22 forms a gullet in the wheel that converges radially inwardly from the base of its respective cutting segment towards an apex.
Preferably the gullet is symmetrical about a line r radiating from the center of the blade through the 15 apex such that the angle A between one side face 22 and radial line r is equal to one half of the included ' angle B between each pair of side faces 20 and 22 forming a respective gullet. It is preferred that angle B be approximately 70, however other angles 20 could bemused. For example, it has been found that the exemplary cutting wheel 1 will function sails-factorial at an angle B greater than 70 provided one does not reach a point where the wheel "hammers"
the materials being cut. I'Hammering'l is the action 25 of a cutting wheel repetitively bouncing off the material surface rather than digging in and cutting it. drill hole I is made approximately at the center point of the apex of each gullet 16 for purposes of relieving stresses which would otherwise be created 30 at a sharp juncture of the side faces 20 and 22.
Figs. 2 and 3 illustrate an exemplary embody-mint of an improved blade or cutting wheel according to the present invention. Similar to the cutting wheel 1 shown in Fig. 1, the cutting wheel 101 gent 35 orally includes a central sheet metal drive disk or core 110 made of suitable wrought metal, preferably ~7~3~

steel, and provided with a central apparatus or arbor hole 112 for mounting the blade on a rotating axially-extending shaft. The periphery of the core is segmented so as to provide a plurality of cutting segments 114 and a gullet 116 between each adjacent pair of cutting segments 114.
Upon a base or support surface located at the radial extremity of each cutting segment 114-there is bonded a diamond-bearing cutting element or member 118.
As viewed from the face of the saw blade looking in an axial direction, the cutting elements are arcuate. The bases of the cutting segments are circular arcs having the center of the drive core as their centers of curvature. The cutting members are composed of diamond grit embedded and dispersed in a hard matrix material such as a mixture of bronze and iron. The particular metal mixture mentioned is preferred at the present time, but it should be understood that the scope of the invention covers any suitable hard abrasive grit dispersed in any suitable hard mixture material. As seen in Figure 2, the cutting members 118 are approximately rectangular in cross section, (as viewed in a circumferential direction), and have a slightly greater width in an axial direction than the core lo to extend axially outwardly beyond the surfaces of the core lo by a small equal amount at either side. The diamond bearing elements or sections 118 are wider than the body of the core lo to provide clearance during cutting, acting similar to the "set" on a wood or metal cutting saw blade.
Although not shown, the cutting members may overlap the peripheral edge of the core at the bottom edges of the grooves in a radially inward direction to a small extent. This overlapping contributes to the prevention of undercutting during the rotating operation of -the saw blade.
In the case of continued use of saw blades of the general type herein I

described, difficulties have been encountered with the drive core being worn out at the region of the arcuate junction of the diamond containing cutting members to the core. This wear is caused by the abrasive action of loose abrading particles on the rotating cutting wheel at this region which sharpens and thins the core at this critical peripheral area. This sharpening and cutting of the metallic periphery of the core may weaken the bonding junction.
The gullets are bounded and defined in part by respective side faces 120 and 122 of each adjacent pair of cutting segments. Each pair of side faces 120 and 122 preferably forms a generally U-shaped gullet with a semi-circular radiuses, or other arcuate, face portion 124 at the closed end of the gullet. Preferably the gullet is symmetrical about a line r radiating from the center of the blade through the gullet such that the distance D between one side face 120 and radial line r is generally equal to the distance between the other side face 122 and the radial line r.
It is preferred that the side faces 120 and 122 are generally straight lines that are generally parallel to the radius line r and hence to each other. It is also preferred that the gullet depth d, which is the radial distance between the open and closed ends of the gullet, is approximately equal to the arc length L' of the gullet. I-t should be noted, however, that gullets having somewhat arcuate side faces, for example, merging with -the radiuses or other arcuate inward portion 124 may also be employed to provide a substantially large volumetric gullet capacity according to the principles of the invention as described herein.
In the preferred embodiment of the present invention, the side faces 120 and 122 are substantially linear and straight in configuration, as mentioned above. It is also preferred that at least at their intersections Jo with the preferably semi-circular arcuate face -portions 124, the side faces 120 and 122 are substantially colinear with tangent lines on the respective sides of the face portion 124. Thus in -this preferred embodiment, as well as in other embodiments, it is desired that the surfaces of the drive core that define the gullet opening (e.g., the side faces 120 and 122, and the arcua-te face portion 124) are substantially continuous with one another and merge together to form a relatively smooth, continuous gullet face in order to substantially minimize the stress concentrations on the drive core during the cutting operation.
In addition to the geometric shape of the gullet, another important criteria -to -the effective performance of -the present invention is that -the total peripheral or circumferential length of diamond bearing material, i.e. the total circumferential length of all members 118, should be approximately equal to, or perhaps slightly greater than, the total gullet arc length or circumferential gullet width at the extremities of the wheel. Thus there is afforded a balance between the cutting ability of-the diamond bearing members and the substantially large volumetric capacity of-the generally U-shaped gullets and thus their ability to circulate fluid to cool the blade and carry away the swarm. Preferably the cutting member arc length L of each cutting member is approximately equal to the arc length L' of each gullet. However, an acceptable approximate range for the ratio of cutting member arc length to gullet arc length is 0.75 to 1.20.
A specific example of an actually-tested very soon of the preferred embodiment is a cutting wheel having the following specifications:
Blade core diameter: 24-1/2 inches (62.2 cm) (nominal 24 inch blade) (61.0 cm) Blade core material: Steel Blade core thickness: 0.125 inches (0.32 cm) Number of cutting members: 19 (equally spaced Cutting member arc length (L): Approx. 2.0 inches (5.1 cm) Number of gullets: 19 Gullet arc length (L'): Approx. 2.0 inches (5.1 cm) (this exact dip mention is determined by the other parameters given in this example) Gullet depth: Approx. 2.0 inches (5.1 cm) The end result of the testing of a blade con-strutted as described above in accordance with the 20 preferred embodiment is a blade wherein the gullet (i) provides a substantially large volumetric entrapment of a fluid coolant within the plane of the blade; (ii) pumps or circulates the fluid coolant into and from the cutting area; (iii) exposes a substantial amount 25 of the core to the coolant; (iv) carry away the swarm from the cutting area each time it passes through the cut; and a blade that has other unexpected superior performance characteristics.
In use, as shown in Fig. 4, the cutting wheel 3Q 101 according to the present invention is mounted on the drive arbor shaft of a saw 50. The saw includes a motor generally shown a-t 52 for driving an arbor shaft 54 and thus the blade 101. It also includes means shown schematically at 56 for continuously providing 35 a fluid coolant under constant pressure to the blade ~22~7~33~

cutting area via a hose 58 leading to the blade shroud 60. The saw apparatus 50 by itself as shown and described is of standard construction and forms no part of the present invention. However, as a result 5 of the unique structure of the cutting wheel or blade 101 itself, upon supplying coolant to the cutting area during the process of cutting an adradable rock material, each gullet 116 in effect renders a very effective or circulating action to the coolant in 10 the cutting area in the manner as elsewhere described herein. This circulating action includes entrapping a substantial amount of the fluid coolant within each gullet as each such gullet enters the immediate area of the cut (i.e. the leading end of the groove being 15 cut, and carrying the coolant from the surface of the material to that area. Thereafter each gullet as it passes from the leading end of the groove being cut entraps a substantial amount of the swarm and carry it away from this area. On at least con-20 lain applications, it is believed the coolant and/orswarf may he caused to flow radially inwardly into a respective gullet, thus keeping the cut or groove McLean of abraded material and providing-a greater cooling effect to the core of the diamond-bearing 25 cutting members.
It is to be understood that the aforedescribed preferred embodiment is not limiting but is merely illustrative of the invention, and various modifications thereof may be made by one skilled in the art without departing from the scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are de-fined as follows:

1. A rotatable cutting wheel for cutting rock or rock-like material, said cutting wheel com-prising: a circular generally disc-shaped drive core having a plurality of circumferentially extending and circumferentially-spaced support surfaces, each of said support surfaces having affixed thereto for sub-stantially the full circumferential length thereof an abrasive cutting material means capable of cutting an abradable rock or rock-like material; said core having a plurality of generally U-shaped gullets, each said U-shaped gullet therein being defined by the space between each adjacent pair of said support surfaces, said U-shaped gullet extending between a closed gullet end located a substantial radial distance inwardly of said support surfaces and an open gullet end being in communication with the space between said adjacent pair of said support surfaces, the circumferential width of said open gullet end being generally co-extensive with the circumferential length of said space; the ratio of said circumferential length of each said adjacent pair of said support surfaces to the circumferential length of said space being in the range of approximately 0.75 to 1.20, the total cir-cumferential length of said support surfaces being approximately equal to the total circumferential width of said U-shaped gullets at the open end thereof, and the radial distance between the open and closed ends of each said U-shaped gullet closely approxi-mating the circumferential width of each said open gul-let end; whereby each said U-shaped gullet and its respective space between adjacent support surfaces cooperate to define a fluid passageway having a sub-stantial volumetric capacity through which a fluid coolant can be circulated in substantial amounts to the cutting area, can cool the drive core in the area immediately adjacent the abrasive cutting material means, and can carry away swarf therefrom.

2. A rotatable cutting wheel according to claim 1, wherein each of said support surfaces is approximately two inches in circumferential length.

3. A rotatable cutting wheel according to claim l, wherein said abrasive cutting material means includes diamond particles held by and dispersed throughout a matrix material.

4. A rotatable cutting wheel according to claim 3, wherein said abrasive cutting material means includes a plurality of separate cutting segments, one of said cutting segments being bonded to each respective said support surface.

5. A rotatable cutting wheel according to claim 4, wherein the circumferential length of each of said cutting segments is in the range of ap-proximately 1.25 inches to approximately 2.5 inches and the axial width thereof is slightly greater than said drive core at said support surfaces, each said cutting segment being axially centered on a respective said support surface so as to extend axially out-wardly beyond the surfaces of said drive core by a substantially equal amount at either side thereof.

6. A rotatable cutting wheel according to claim 1, wherein each said U-shaped gullet is sub-stantially symmetrical to a line radiating from the center of said core through said U-shaped gullet, said line being generally equidistant from said pair of said faces.

7. A rotatable cutting wheel according to claim 1, wherein each of said U-shaped gullets is de-fined in part by a pair of spaced-apart side faces at opposite sides of said space between said adjacent pair of said support surfaces, said side faces being interconnected by a generally arcuate face portion therebetween at said closed gullet end.

8. A rotatable cutting wheel according to claim 7, wherein said side faces and said arcuate face portion are substantially continuous with an-other in order to form a substantially continuous U-shpaed gullet face, thereby substantially minimiz-ing stress concentrations in said drive core during said cutting of said rock or rock-like material.

9. A rotatable cutting wheel according to claim 8, wherein said generally arcuate face is sub-stantially semi-circular in configuration.

10. A rotatable cutting wheel according to claim 9, wherein said side faces are substantially linear and substantially colinear with respective lines that are tangent to respective sides of said semi-circular arcuate face portion.

11. A rotatable cutting wheel according to claim 10, wherein said linear side faces are sub-stantially parallel to one another and substantially parallel to a radius line equidistant from said linear faces and radiating from the center of said core through said U-shaped gullet.

12. A rotatable cutting wheel according to claim 8, wherein at least a portion of each of said side faces are arcuate in configuration, said gen-erally U-shaped gullet being substantially sym-metrical to a line radiating from the center of said core through said U-shaped gullet, said line being generally equidistant from corresponding radial loca-tions on said side faces.

13. In combination, a machine for cutting natural and artificial rock material including a rotary abrasive cutting means, means for rotating said cutting means about an axis and means for supply-ing a liquid coolant to said cutting means for pur-poses of cooling the cutting means and carrying away loose rock material from the cutting edges thereof, said cutting means including at least one circular generally. disc-shaped drive core; said drive core having a plurality of circumferentially ex-tending and circumferentially spaced support surfaces, each of said support surfaces having affixed thereto for substantially the full circumferential length thereof an abrasive cutting material means capable of cutting an abradable rock or rock-like material;
said core having a plurality of generally U-shaped gullets, each said U-shaped gullet therein being de-fined by the space between each adjacent pair of said support surfaces, each said U-shaped gullet extend-ing between a closed gullet end located a substantial radial distance inwardly of said support surfaces and an open gullet end being in communication with the space between said adjacent pair of said support surfaces, the circumferential width of said open gul-let end being generally coextensive with the cir-cumferential length of said space; the ratio of said circumferential length of each said adjacent pair of said support surfaces to the circumferential length of said space being in the range of approximately 0.75 to 1.20, the total circumferential length of said support surfaces being approximately equal to the total circumferential width of said U-shaped gullets at the open end thereof, and the radial distance between the open and closed ends of each said U-shaped gullet being approximately equal to the circumferential width of each said open gullet end; whereby each said U-shaped gullet and its respective space between ad-jacent support surfaces cooperate to define a fluid passageway having a substantial volumetric capacity through which a fluid coolant can be circulated in substantial amounts to the cutting area, can cool the drive core in the area immediately adjacent the ab-rasive cutting material means, and can carry away swarf therefrom.

14. The combination according to claim 13, wherein said abrasive cutting material means includes diamond particles held by and dispersed throughout a matrix material.

15. The combination according to claim 13, wherein said abrasive cutting material means com-prises a plurality of separate cutting segments, one of said cutting segments being bonded to each re-spective said support surface.

16. The combination according to claim 15, wherein each said cutting segment is approximately two inches in circumferential length and the axial width thereof is slightly greater than said drive core at said support surfaces, each said cutting segment being axially centered on a respective said support surface so as to extend axially outwardly beyond the surfaces of said drive core by a substantially equal amount at either side thereof.

17. The combination according to claim 13, wherein each of said U-shaped gullets being defined in part by a pair of spaced-apart side faces at opposite sides of said space between said adjacent pair of said supporting surfaces, said side faces facing in generally circumferential directions toward one another and being interconnected at said closed gullet end by a generally arcuate face portion.

18. The combination according to claim 17, wherein said side faces and said arcuate face portion are substantially continuous with one another in order to form a substantially continuous U-shaped gullet face, thereby substantially minimizing stress con-centrations in said drive core during said cutting of said rock or rock-like material.

19. The combination according to claim 18, wherein said side faces are substantially linear and said arcuate face portion is substantially semi-circular, said side faces being substnatially co-linear with lines extending tangentially from re-spective sides of said semi-circular arcuate face portion.

20. The combination according to claim 19, wherein said linear side faces are substantially parallel to one another and substantially parallel to a radius line extending through said axis and through said U-shaped gullet at a position equidistant from said linear side faces.

21. The combination according to claim 18, wherein at least a portion of each of said side faces are arcuate in configuration, said generally U-shaped gullet being substantially symmetrical to a line radiating from said axis through said U-shaped gullet, said line being generally equidistant from corresponding radial locations on said side faces.

22. A rotatable cutting wheel for cutting rock or rock-like material, said cutting wheel comprising:
a generally circular disc-shaped drive core having a number of circumferentially-extending and circum-ferentially-spaced support surfaces thereon, each of said support surfaces having cutting means affixed thereon; said core having a number of generally U-shaped gullet openings, each of said generally U-shaped gullet openings being defined by the space between adjacent pairs of said support surfaces and having an open end and a closed end, the circumferen-tial width of said space between adjacent support surfaces being approximately equal to the circumfer-ential length of each of said support surfaces, the radial depth of each of said generally U-shaped gullets being approximately equal to the circumfer-ential width of said space between adjacent support surfaces; each of said generally U-shaped gullets having a pair of spaced-apart side faces at opposite sides of said space between said adjacent pair of support surfaces, the circumferential distance between said side faces being at least as large as said cir-cumferential width of said space between said ad-jacent support surfaces along a substantial portion of said side faces; whereby each of said generally U-shaped gullets and its respective space between adjacent support surfaces cooperate to define a fluid passageway having a substantial volumetric capacity through which a fluid coolant can be circulated in substantial amounts to the cutting area of said cut-ting wheel, can cool the drive core in the area im-mediately adjacent the cutting means, and can carry away swarf therefrom.

23. A rotatable cutting wheel according to

claim 24, wherein each of said generally U-shaped gullets is defined at least in part by a pair of spaced-apart side faces at opposite sides of said space between said adjacent support surfaces and by a generally arcuate face portion interconnecting said side faces at said closed gullet end.
24. A rotatable cutting wheel according to claim 23, wherein said side faces are substantially linear and substantially parallel to one another, said arcuate face portion being substantially semi-circular in configuration, said side faces further being substantially colinear with respective lines tangent to respective sides of said semi-circular arcuate face portion.

25. A rotatable cutting wheel according to claim 24, wherein said side faces are each substan-tially parallel to a line radiating from the center of said drive core and extending through said gen-erallY U-shaped gullet opening at a position equi-distant from said side faces.

26. A rotatable cutting wheel according to claim 24, wherein the circumferential length of each of said support surfaces is in the range of approxi-mately 1.25 inches to approximately 2.5 inches.